1. Field of the Invention
The present invention relates, in general, to a guide for and a method of preparing a patella to receive a patellar prosthesis.
2. Background Art
The posterior surface of a healthy patella or knee-cap has two articular facets, lateral and medial, separated by a vertical ridge. The articular facets glide on the lateral and medial condyles of the femur while the vertical ridge fits into the groove between the condyles. Disease or trauma may degenerate or damage the posterior surface of a patella, causing pain and/or immobility of the knee joint. Various patellar implants and prostheses have been developed to replace the articulating surface of such patellas. See, for example, Whiteside et al., U.S. Pat. No. 5,019,104, issued May 28, 1991.
A patellar implant may be recessed into the posterior surface of a patella to help reproduce the patient's original patellar dome location and height while maintaining as much bone stock as possible. Such patellar implants are provided in different thicknesses and diameters. For example, patellar implants may be provided in various thicknesses ranging between 7 and 10 millimeters and in various diameters ranging between 25 and 32 millimeters to allow optimal patella repair.
An end mill, reamer or other cutting tool is typically used to recess or resect the posterior surface of the patella. If possible, the full thickness of the selected patellar implant should be removed from the patellar surface. Guides consisting of metal rings may be clamped onto the posterior surface of the patella to act as a stop to allow an end mill or the like to be inserted only a specific depth into the posterior surface of the patella, depending on the thickness of the ring.
Nothing in the known prior art discloses or suggests the present invention. For example, nothing in the known prior art discloses or suggests an adjustable depth patella recessing guide including a body having a first end for engaging the posterior surface of the patella, having a second end, and having a bore extending between the first and second ends for allowing the cutting tool to pass therethrough; a depth gauge mounted within the bore of the body for movement in a direction between the first and second ends of the body, the depth gauge including stop means for stopping the cutting tool; and lock means for locking the depth gauge to the body. Likewise, nothing in the known prior art discloses or suggests a method of recessing the posterior surface of a patella by clamping the body of the adjustable depth patella recessing guide to the posterior surface of the patella; placing the distal end of the cutting tool against the posterior surface of the body; then ascertaining the position of the cutting tool relative to the body; then locking the depth gauge to the body so that the depth gauge will stop the cutting tool a certain distance past the ascertained position of the cutting tool relative to the body; and then inserting the cutting tool into the posterior surface of the patella until stopped by the depth gauge.